Half-blood is the term commonly given to wizards and witches who have a Muggle/Muggle-born parent and magical parent. By the 1990s, half-bloods were the most common type of magical person, as the wizarding population would have become extinct had they not inter-married with Muggles and Muggle-borns.[1]

Due to the dominance of the magic gene, children born to at least one magical parent will almost always be magical themselves. A non-magical child born to a Muggle and a wizard is considered a Squib (not a Muggle).[2]

Some half-bloods expressed prejudice towards those with Muggle heritage, despite having some themselves, and clung to what wizarding heritage they had. Notably, Lord Voldemort hated Muggles and Muggle-borns, despite having a Muggle father, and denied his half-Muggle heritage, leaving hints that he was a pure-blood instead, emphasizing his heritage to the famous pure-blood ancestor, Salazar Slytherin, to make himself more believable.[1]Severus Snape may be another example; his self-entitled nickname was "Half-Blood Prince" because his mother, Eileen Prince, was a pure-blood witch and his father, Tobias Snape, was a Muggle. However, Remus Lupin reported that he never used the nickname openly. This, as well as Snape's membership in the Death Eaters, suggests he may have been ashamed of his Muggle heritage, at least in his early life.[4] In fact, these people, along with some other Death Eaters, pretend to be pure-bloods, hiding their Muggle heritage from anyone else; most of them are half-bloods due to centuries of dilution and decline of what may be called as a true "pure-blood". Ironically (or perhaps because of), regarding the Prophecy concerning his defeat, Voldemort chose to go after a half-blood Harry Potter instead of the pure-blood Neville Longbottom.

On the draft class list, Hannah Abbott was listed as a Muggle-born[9], but in a later interview, Rowling stated that she had always thought of Hannah as a pure-blood. To compromise, she was made a half-blood.[10]